1. Field of the Invention
The present invention relates to an active headrest apparatus for a vehicle seat having an improved structure in which neck injury of a person who is seated in a car can be prevented to the maximum in the event of a rear-end collision of the car.
2. Description of the Related Art
Generally, seats for vehicles should be comfortable when a person is seated in a car and should protect the person who is seated in the car when the person has an emergency, such as a rear-end collision of the car.
Seat for vehicles include a seat cushion that supports the lower body of the person who is seated in the car, a seat back that supports the upper body of the person who is seated in the car, and a headrest that is combined to a top end of the seat back so that the height of the headrest can be adjusted in a vertical direction, and that supports head and neck of the person who is seated in the car.
In the event of a rear-end collision of the car that stops, neck injury of the person who is seated in the car occurs frequently. This case is called whiplash injury.
It is known that such whiplash injury, i.e., neck injury is caused by a difference in relative speed between the upper body and the head of the person who is seated in the car. Thus, while the upper body of the person who is seated in the car is moved forward due to shock of the seat back during the rear-end collision, the head of the person is kept in its original position, and a shearing force exerts on the neck of the person. The shearing force causes severe shock to the joint and muscle of the neck and injury of the joint of the neck.
To prevent the problems, an active headrest that allows a headrest to be moved to be adjacent to the head of the person during the rear-end collision has been developed, and there is a trend for reducing neck injury of the person who is seated in the car by using the active headrest.
The active headrest is generally configured to allow a driving unit included in the seat back to operate by a pressure applied by the upper body of the person who is seated in the car. While the active headrest is maintained to be inclined about 5° with respect to a seat back frame in a direction to the person who is seated in the car, the active headrest is moved toward the head of the person who is seated in the car and supports an occipital area of the person who is seated in the car.
FIG. 1 illustrates a conventional active headrest apparatus. Referring to FIG. 1, right and left ends of a back plate 1 to which a pressure is applied by the upper body of a person who is seated in a car, are combined to both end portions of a lower armature 2 as one body. An armature bracket 3 is securely combined to both end portions of the lower armature 2. Frame brackets 5 are securely combined to both side frames 4a that constitute a seat back frame 4, respectively. Link brackets 6 are rotatably combined to the armature bracket 3 and the frame bracket 5 via a hinge pin 7 and a pivot pin 8, respectively. The side frames 4a and the link brackets 6 are connected to each other via a spring member 9, and a pair of upper armatures 10 that are combined to the lower armature 2 as one body perforate a guide hole 4c formed in an upper frame 4b that connects the side frames 4a. 
Thus, when the upper body of the person who is seated in the car pressurizes the back plate 1 backward due to an inertial force generated during a rear-end collision, the link bracket 6 is rotated around the pivot pin 8. As such, the back plate 1 is moved backward along a rotational radius of the link bracket 6 and rises, and simultaneously, the upper armature 10 perforates the guide hole 4c and protrudes upward.
Then, a headrest stay 11 inserted in the upper armature 10 and fixed thereto is moved and rises, and a headrest 12 combined to the headrest stay 11 is moved and rises forward in a direction to the head of the person who is seated in the car and supports an occipital area of the person who is seated in the car, thereby performing a function of an active headrest.
However, in the conventional active headrest apparatus illustrated in FIG. 1 described above, the frame bracket 5 combined to the side frames 4a protrudes toward an inside of the seat back frame 4. Thus, when the upper body of the person who is seated in the car is moved backward due to the inertial force in the event of the rear-end collision, the seat back frame 4 interferes with the frame bracket 5.
Thus, a contact area in which the upper body of the person who is seated in the car contacts the back plate 1 is decreased. When the contact area is decreased, a pressure applied to the back plate 1 is reduced. When the pressure is reduced, a distance at which the back plate 1 is moved backward is decreased, and when the distance at which the back plate 1 is moved backward is decreased, a degree at which the upper armature 10 perforates the guide hole 4c and protrudes upward is reduced. This causes a reduction in a distance at which the headrest 12 is moved forward and rises in a direction to the head of the person who is seated in the car, so that the headrest 12 cannot faithfully perform the function of the active headrest.
FIG. 2 illustrates another conventional active headrest apparatus. Referring to FIG. 2, the active headrest apparatus includes a guide member 13 including guide grooves 13a respectively combined to insides of the side frames 4a, a back plate 1 in which guide pins 14 that are inserted in the guide grooves 13a and move along the guide grooves 13a are combined to right and left end portions of the back plate 1, respectively, and a spring member 9 that connects the side frames 4a and the back plate 1 to each other.
However, even in the conventional active headrest apparatus illustrated in FIG. 2, since the guide member 13 protrudes toward an inside of the seat back frame 4a, the same problem as the conventional active headrest apparatus illustrated in FIG. 1 occurs.
If the guide member 13 is removed and the guide grooves 13a are formed directly in the side frames 4a, the conventional problems described above may be overcome. However, in that case, the strength of the side frames 4a is greatly reduced, and due to the side frames 4a with the reduced strength, the overall strength of the seat back frame 4 is decreased, so that there is a possibility that another problem that the seat back frame 4 is easily destroyed due to shock caused by the rear-end collision and the safety of the person who is seated in the car is threatened, may occur. Thus, it is not desirable to directly form the guide grooves 13a in the side frames 4a. 